This invention relates generally to a vehicle door latch and more particularly to a vehicle door latch that has a forkbolt, a detent for holding the forkbolt in a latched position, a release mechanism for moving the detent to a position releasing the forkbolt and a lock mechanism for disabling the release mechanism.
An automotive closure, such as a door for an automobile passenger compartment, is hinged to swing between open and closed positions and conventionally includes a door latch that is housed between inner and outer panels of the door. The door latch functions in a well known manner to latch the door when it is closed and to lock the door in the closed position or to unlock and unlatch the door so that the door can be opened manually.
In general terms, the door latch has a forkbolt that engages a striker in the door jamb to latch the door when it is closed and a spring biased detent that engages and holds the forkbolt in the latched position. The door latch also typically has a release mechanism for moving the detent to a position releasing the forkbolt so that the door can be unlatched and opened and a lock mechanism for disabling the release mechanism to prevent unauthorized unlatching of the door.
Door latches often use soft thermoplastic materials and bumpers to enhance the sound quality of the door latch, particularly that of the operations of the forkbolt and the detent. See for instance, U.S. Pat. No. 5,277,461 granted to Thomas A. Dzurko et al Jan. 11, 1997 for a vehicle door latch, which discloses a typical door latch of the above noted type. The door latch disclosed in the Dzurko ""461 patent includes a forkbolt that has a plastic coating that covers a surface of a slot that is engaged by the striker for energy absorption and quiet operation when the door is slammed shut. The detent lever also includes a plastic coating which has a slotted portion that provides an integral bumper that engages a stop to absorb energy and quiet operation when the door is slammed shut.
Door latches of the type disclosed in the Dzurko ""461 patent have been used successfully by automotive manufacturers for many years. However, there is a desire to make further improvements in the door latches of the above noted type with regard to quiet operation.
The object of this invention is to provide a vehicle door latch that is quiet in operation.
It is well known that the noise produced by the spring biased detent striking the forkbolt to engage and hold the forkbolt in the latched position is detrimental to quiet operation of the door latch, particularly the latching sound that is produced when the door is slammed shut. We have found that level of noise of the latching sound is related to the acceleration of the spring biased detent as it moves from the release position to the detent position and strikes the forkbolt under the bias of the detent spring.
The door latch of the invention has a main detent spring and an auxiliary detent spring that act in concert so the detent decelerates faster as the detent approaches the forkbolt. This softens the sound because the energy is dissipated over a larger time domain resulting in quiet operation even when the striking surfaces are metal. The auxiliary spring also results in a reduced unlatching effort without any impact in meeting performance requirements for maintaining the detent in a primary or secondary latch position.
In a preferred embodiment, the auxiliary spring takes the form of a counter spring that acts against the main detent spring during the ending portion of the detent stroke as the detent moves from the release position to the detent position. In another preferred embodiment, the auxiliary spring takes the form of a helper spring that assists the main detent spring during the initial portion of the detent stroke.
In either event, the auxiliary spring is preferably a metal spring because the performance of the metal auxiliary spring is more stable in comparison to the use of thermoplastic materials because the performance of the counter spring does not change nearly as much as the thermoplastic materials from a time and temperature perspective.